INORGANIC CONSTITUENTS OF THE URINE. 387 



united with the nitrogenized constituents of the organism, and when these 

 are changed into excrementitious substances and are separated from the blood 

 by the kidneys, they pass with them and are discharged from the body. 



It is a question of some importance to consider how far the phosphates 

 are derived from the tissues and what proportion comes directly from the 

 food. All observers agree that the quantity of phosphates in the urine is in 

 direct relation to the proportion in the food, and that an excess of phos- 

 phates taken into the stomach is immediately thrown off by the kidneys. It 

 is a familiar fact, indeed, that the phosphates are deficient and the carbonates 

 predominate in the urine of the herbivora, while the reverse obtains in the 

 carnivora, and that variations, in this respect, in the urine, may be produced 

 by feeding animals with different kinds of food. Deprivation of food 

 diminishes the quantity of phosphates in the urine, but a certain proportion 

 is discharged, which is derived exclusively from the tissues. 



In connection with the fact that phosphorus exists in the nervous mat- 

 ter, it has been assumed that mental exertion is always attended with an in- 

 crease in the elimination of phosphates ; and this has been advanced to sup- 

 port the view that these salts are specially derived from disassimilation of the 

 brain-substance. Experiments show that it is not alone the phosphates that 

 are increased in quantity by mental work, but urea, the chlorides, sulphates 

 and inorganic matters generally; and in point of fact, any physiological 

 conditions which increase the proportion of nitrogenized excrementitious 

 matters increase as well the elimination of inorganic salts. It can not be 

 assumed, therefore, that the discharge of phosphates is specially connected 

 with the activity of the brain. Little has been learned upon this point from 

 pathology, for although many observations have been made upon the excre- 

 tion of phosphoric acid in disease Vogel having made about one thou- 

 sand different analyses in various affections no definite results have been 

 obtained. From these facts it is seen that there is no physiological reason 

 why the elimination of the phosphates should be specially connected with 

 the disassimilation of any particular tissue or organ, especially as these salts 

 in some form are universally distributed in the organism. 



Observations have been made upon the hourly variations in the discharge 

 of phosphoric acid at different times of the day ; but these do not appear to 

 bear any definite relation to known physiological conditions, not even to the 

 process of digestion. 



Of the different phosphatic salts of the urine, the most important are 

 those in which the acid is combined with sodium. These exist in the form 

 of the neutral and acid phosphates. The acid salt is supposed to be the 

 source of the acidity of the urine at the moment of its emission. The so- 

 called neutral salt is slightly alkaline. The proportion of the sodium phos- 

 phates in the urine is larger than that of any of the other phosphatic salts, 

 but the daily quantity excreted has not been estimated. According to Robin, 

 there always exists in the urine a small quantity of the ammonio-magnesian 

 phosphate, but it never, in health, exists in sufficient quantity to form a crys- 

 talline deposit. The daily excretion of the phosphates is subject to great 



